The purpose of this paper is to present a brief overview of the nature of pedagogical content knowledge and to offer a list of working hypotheses concerning it for incorporation into teacher education programs. What teachers know about teaching, such as preinstructional strategies, the use of concrete examples and manipulatives, formative testing, use of questions, design of curriculum and assignments, and assessment of student performance, comprises pedagogical knowledge. Pedagogical content knowledge is a type of knowledge unique to teachers; it concerns the manner in which teachers relate their pedagogical knowledge to their subject matter knowledge in the school context, for the teaching of specific students. The integration of teachers' pedagogical knowledge and their subject matter knowledge comprises pedagogical content knowledge. This paper summarizes the state of current research and describes a tentative model for use in teacher preparation programs. A list of working hypotheses based on current knowledge is presented to serve as a basis for future theoretical and applied research. (LL)